【技能库】--Unsafe 调戏String (intern) (201)

来源：互联网发布：火狐浏览器mac版编辑：程序博客网时间：2024/05/29 14:45

1 通过反射获取unsafe实例

2 获取char[]数组变量偏移地址
3 获取实例char[]

4 unsafe --> (arrayBaseOffset)第一个元素位置和每个元素大小(arrayIndexScale) 修改数组

5 代码如下

    public static Unsafe getUnsafeInstance() throws Exception{        Field unsafeStaticField =                Unsafe.class.getDeclaredField("theUnsafe");        unsafeStaticField.setAccessible(true);        return (Unsafe) unsafeStaticField.get(Unsafe.class);    }    public static void main(String[] args) throws Exception {    String s = "abc";//      s.intern();//JDK 8 自动        String s1 = "abc";        Unsafe u = getUnsafeInstance();//获取变量value        Field valueInString = String.class.getDeclaredField("value");//获取value的变量偏移值        long offset = u.objectFieldOffset(valueInString);//获取value        char[] values = (char[]) u.getObject(s1, offset);//value本身是一个char[],要修改它元素的值，仍要获取baseOffset和indexScale        long base = u.arrayBaseOffset(char[].class);        long scale = u.arrayIndexScale(char[].class);//为value赋值        u.putChar(values, base + scale, 'c');        System.out.println("s:"+s+" s1:"+s1);        String s2 = "abc";        System.out.println("s="+s+" s1="+s1+" s2="+s2);}

0 0